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Ann Thorac Surg 2002;74:S1348-S1352
© 2002 The Society of Thoracic Surgeons
a Cardiac Surgery, San Raffaele University Hospital, Milan, Italy
* Address reprint requests to Dr Torracca, Via Olgettina 60, 20132 Segrate, Milan, Italy
e-mail: lucia.torracca{at}hsr.it
Presented at the Eighth Annual Cardiothoracic Techniques and Technologies Meeting 2002, Miami Beach, FL, Jan 23–26, 2002.
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Abstract |
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METHODS: In 8 patients with multivessel coronary disease who were undergoing to off-pump coronary artery bypass grafting, LV performance was analyzed from the pressure–volume (P-V) plane by the conductance catheter technique. Measurements were performed at base line, after the exposure of the vessels, after the application of the stabilization system, and at the end of the procedure.
RESULTS: No significant changes in heart rate, LV end-systolic volume, LV end-diastolic pressure, mean pulmonary artery, and mean systemic blood pressure were observed in the various stages of the procedure. Cardiac index decreased during left anterior descending coronary artery grafting after application of the stabilizer with a concomitant decrease in LV end-diastolic volume, together with decreases in LV peak negative -dP/dt and increases in 
, indicating an impairment of LV relaxation but without a change in preload recruitable stroke work, indicating preserved LV contractile state. Exposure of posterior and lateral vessels induced a decrease in cardiac index and preload recruitable stroke work without a decrease in LV preload, indicating a decrease in LV contractile state together with a decrease in peak -dP/dt and increase in , indicating an impairment in LV relaxation
CONCLUSIONS: Off-pump coronary artery bypass grafting can be performed without decreasing LV performance. Major cardiac displacement like that used for posterior and lateral exposure induces acutely significant decrease in LV contractile state.
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Therefore, we studied the hemodynamic changes occurring during heart displacement and coronary stabilization for OPCABG by analysis of the LV pressure–volume plane during the different phases of the procedure [12].
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Anesthesia
All patients received 0.05 mg/kg of lorazepam orally as premedication 2 hours before surgery. Anesthesia was induced with Diprivan (AstraZeneca, Wilmington, DE) and maintained by Diprivan and isoflurane. For muscle relaxation, 0.1 mg/kg of pancuronium bromide was given. The patients were ventilated with an oxygen/air mixture (FiO2 = 0.5) at a ventilator rate of 12 per minute, and ventilatory volume was adjusted to maintain arterial CO2 tension between 32 and 42 mm Hg.
All patient were treated with circulatory volume expansion, achieving a mean pulmonary artery pressure of 20 mm Hg before OPCABG. All patients received equal small dosages of nitroglycerin throughout the procedure. One patient received an equal small dose of dopamine throughout all series.
Instrumentation
A Swan-Ganz thermodilution catheter was placed through the internal jugular vein or subclavian vein into the pulmonary artery. A micromanometer transducer conductance catheter (F7, Sentron, CD Leycom, Zoetermeer, the Netherlands) was inserted through the right upper pulmonary vein into the left ventricle, for measurement of LV pressures and LV volumes. The feasibility of the conductance catheter method during cardiac surgery has been shown in a previous study [13]. The correct position of the conductance catheter was verified by TEE and by inspection of the segmental conductance signals. The conductance catheter was connected to a Leycom CFL 512 cardiac function analyzer (CD Leycom) to measure instantaneous LV and segmental volumes [12, 13]. The dual-field excitation mode, which has been shown to improve accuracy of the method, was used in all patients [14].
The conductance catheter measures the instantaneous volumes of five ventricular segments delineated by selected catheter electrodes. It has been shown previously that the time-varying segmental conductance reflect time-varying segmental LV volume as obtained by cine computed tomography in canine hearts [15]. Total volume is calculated as the sum of the segmental volumes.
The conductance catheter continuously measures not only the relative amount of blood in the LV, but also the conductance of the myocardium and other surrounding tissues, the parallel conductance. This parallel conductance offset term (Vc) for the LV was estimated by injection of 7.5 mL hypertonic saline (6%) into the pulmonary artery [12]. The Vc estimation was performed by the dedicated software package CONDUCT-PC (CD Leycom). The implemented algorithm finds the best Vc values, thus avoiding an operator-dependent bias. At each stage of the procedure the parallel conductance measurements were performed twice. To get absolute volumes with the conductance catheter technique, the effective conductance stroke volume (SV) must be matched with a gold-standard SV measurements technique. Therefore, cardiac output was determined at each stage of the procedure by performing five thermodilution measurements, using a cardiac output computer (COM-2, Baxter, Deerfield, IL), and using injections of 10 mL of ice-cold glucose 5%. Consequently absolute LV volumes were calculated by matching effective conductance SV with simultaneously measured thermodilution SV, and by subtracting the parallel conductance correction volume from total conductance volume.
Data acquisition and analysis
Electrocardiographic (extremity leads), aortic pressure, LV pressure, and LV volume signals were digitized at a sampling rate of 250 Hz and stored on hard disc for subsequent analysis. The dedicated data acquisition and analyses software package CONDUCT-PC was applied for conductance catheter–related data analysis. In addition to the volumetric variables, pressures, and peak first derivatives, the following variables were calculated: , the time constant of LV pressure relaxation, which was defined as the time required from the LV pressure at the peak -dP/dt to be reduced by half; peak ejection rate, and peak filling rate, calculated as maximal -dV/dt and maximal dV/dt, respectively.
Effective LV ejection fraction was calculated from the thermodilution-derived SV and the LV end-diastolic volume measured by the conductance catheter.
Surgical technique
After harvesting of the conduits, the feasibility of the procedure was assessed by exploring the coronary arteries.
The left anterior descending coronary artery (LAD) was exposed by placing moistened gauze pads behind the left ventricle and making traction on the left border of the pericardium to elevate and rotate the heart.
Exposure of the lateral and inferior wall vessels was obtained by traction of a stitch placed in the deepest part of the pericardium between the pulmonary veins [5]. The right pleura was opened to minimize the inferior vena cava and right atrium compression and to allow normal heart filling. Vessel exposure was completed by rotating the operating table. When adequate vessel exposure was achieved, the stabilization system was applied. In 4 patients, stabilization of the anastomotic site was achieved by a suction system (Octopus 3; Medtronic, Inc, Minneapolis, MN); in the other 4 patients, a compression stabilization system (OPCAB Immobilizer, Genzyme, Cambridge, MA) was used. All anastomoses were performed using intracoronary shunt devices
Measurement protocol
Hemodynamic data were obtained at base line with the heart in physiologic position, after the heart displacement for vessels exposure (positioning [pos] 1a = LAD set-up, pos 1b = inferior and lateral vessels set-up) and after the placement of the stabilizer (pos 2a and 2b). Base line data were recorded again at the end of each anastomosis, with the heart in the normal position. The patients were placed in head-down position during pos 2.
Because the surgical procedure and the changes in preload and afterload may affect catheter position and parallel conductance, we performed the following measurements to calibrate the conductance catheter. At each stage of the procedure we determined parallel conductance in duplicate, and cardiac output by themodilution (four injections). Steady-state pressure–volume (P-V) loops were acquired during at least 15 seconds during suspended ventilation.
Statistical analysis
Data are presented as mean ± standard deviation. For comparison or base line data obtained during heart displacement, a paired Student’s t test was used. A p value of less than 0.05 was considered to indicate a statistically significant difference.
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Results |
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Figure 1 shows P-V loops of 1 patient measured before, during, and after pos 2, revealing no major changes in LV end-diastolic volume. During the heart lifting (pos 2) the P-V loops of this patient show characteristics of aortic regurgitation, which disappeared at base line 2.
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; decreased (p < 0.01) and increased (p < 0.01) respectively at position 1b and position 2a and 2b, indicating hampered LV relaxation. The calculated single loop contractility indices preload recruitable stroke work (PRSW), +dP/dt versus end-diastolic volume and end-systolic pressure versus end-diastolic volume did not change during pos 1; however, all were decreased (p < 0.01) during pos 2b, indicating a preserved LV contractile state despite the impairment of LV relaxation during pos 1b, and decreased contractile state combined with impaired LV relaxation during pos 2b.
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Comment |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Different systems can be used to stabilize the anastomotic site. Suction or compression systems are usually applied, with potentially different consequences on the hemodynamic values.
Exposure of the LAD has no major hemodynamic consequences. However, after application of a stabilizer, a significant decrease in CI and SV was observed. These changes were associated with a significant reduction of the end-diastolic volume. However, both peak -dP/dt and , indices of LV relaxation were impaired after application of the stabilizer. These changes can be explained by local LV compression, which invariably occurs even with a suction device, between the gauze pads behind the ventricle and the stabilization system on the anterior wall. The impaired LV relaxation may have contributed to the lower end-diastolic volume by impeding diastolic filling, which was not compensated by a head-down position.
Exposure of the inferior and lateral wall vessels can only be obtained with a major heart displacement by verticalization of the long axis of the heart. During this exposure, a significant reduction in cardiac index (CI) an SV was observed, whereas end-diastolic volume or the LV preload remained unchanged. Peak -dp/dt and , the relaxation indices, both deteriorated, impairing the diastolic filling. Probably the Trendelenburg position compensated for the decrease in LV end-diastolic volume due to the impairment of LV relaxation.
After placement of the stabilizer, a further decrease in CI and further impairment of LV relaxation occurred. Moreover, at this stage, all contractility indices were significantly decreased. These finding confirm the decrease in CI even with a preload similar to the base line condition.
These important hemodynamic changes can probably be explained by alterations in the geometry of the heart due to verticalization. In this position, the ventricular mass leans on the atrioventricular valves, which can even become insufficient, as documented by echocardiography. Verticalization of the heart, by creating an angle between the base and the apex of the heart, may also produce outflow obstruction or may induce aortic regurgitation, as can be derived from Figure 1.
All of the hemodynamic changes recorded during displacement of the heart and application of the stabilizers were well tolerated and transient. Base line values were resumed at the end of the procedure, with the heart in physiologic position.
Two patients of this study had low LV ejection fractions, but their hemodynamic responses were similar to those of the patients with higher ejection fraction.
In conclusion, major heart displacement, which is necessary to expose vessels during beating heart coronary surgery and application of stabilizers, is associated with marked deterioration of LV performance. Nevertheless, the procedure is well tolerated, and the hemodynamic changes are transient and reversible.
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